Mineral fiber insulation is well known and has been a commercial product for an extended period of time. Such insulation typically is made from a nonwoven network of intertwined fibers that have been fiberized from a melt, by one of several processes discussed below, and that are held together by a binder. The binder may be any suitable material but quite commonly is a phenol-formaldehyde resin or a ureaformaldehyde resin. A conveyor typically collects the binder-coated fibers in the form of a blanket and the blanket is heat cured to produce the final insulation product. Insulation materials of various densities can be produced by varying the conveyor speed and the thickness of the cured insulation.
Glass wools are generally prepared by a rotary process, whereby a glass melt is dropped into a "spinner" having a peripheral wall having a multitude of holes therein, through which the glass is forced by centrifugal force to form fibers, which process gives excellent fiber yields, i.e., low "shot" contents and excellent insulating properties. However, the glasses used to produce these fibers have low softening temperatures so that their use is generally limited to only moderately high service temperatures.
Mineral wools, on the other hand, have higher softening and use temperatures and thus can typically be used in higher temperature environments. However, these compositions generally have forming temperatures which are too high for rotary fiberizing. Mineral wools are usually formed by external centrifuge processes that produce a lower fiber yield and a higher shot content than the rotary process. An example of a mineral wool intended to be fiberized by an external centrifuge process is disclosed in WO 96/00196.
Previously in the art mineral wool compositions have been reported which allegedly can be formed into fiber by a rotary process. (See International Patent Application Publications WO 95/01941 and WO 93/02977, U.S. Pat. No. 5,554,324, and European Patent Application EP 583 792). However, these compositions all contain high amounts of Na.sub.2 O, K.sub.2 O, and B.sub.2 O.sub.3, which can negatively affect the high temperature performance of the fiber, or high amounts of Al.sub.2 O.sub.3, which can decrease the biosolubility of the fiber.
Although mineral fibers have not been linked to disease in humans, it has become desirable to increase the biosolubility of mineral fibers. One would expect that increasing the solubility of mineral fibers would further decrease the time the fibers remain in a lung, if they were to be inhaled, and thus that the dissolution rate of mineral fibers in a saline solution having a composition similar to that existing in a human lung would be a good indicator of the biosolubility of such fibers. This dissolution rate can be improved by altering the chemical composition of a fiber. Previously in the art, it was thought that these alterations could not be made without impairing other properties of the fibers necessary for commercial purposes.
Accordingly, it is an object of the present invention to provide an improved mineral fiber composition and an improved mineral fiber formed from such composition.
Another object of the present invention is to provide a mineral fiber useable in relatively high temperature environments.
A further object of the present invention is to provide a mineral fiber composition that may be formed into a mineral fiber in a rotary fiberizing process.
Yet another object of the present invention is to provide a mineral fiber that is relatively biosoluble, yet sufficiently durable.
More preferably, it is an object of the present invention to provide a mineral fiber composition that may be formed into a mineral fiber in a rotary fiberizing process, which fiber is usable in high temperature environments and is sufficiently durable.
More preferably, it is an object of the present invention to provide a mineral fiber composition that may be formed into a mineral fiber in a rotary fiberizing process, which fiber is usable in high temperature environments and is relatively biosoluble, yet sufficiently durable.